Combination treatment of pancreatic cancer

ABSTRACT

A combination for use in the treatment of pancreatic cancer comprising: (i) an anti-gastrin effective immunogenic composition; and, (ii) one or more chemotherapeutic agents suitable for inhibiting cancer growth.

This application claims the benefit of U.S. provisional patentapplication 60/278,294 filed Mar. 23, 2001.

FIELD OF THE INVENTION

The invention relates to a combination of immunological andchemotherapeutic treatment of pancreatic cancer. In particular,treatment of locally advanced or metastatic gastrin-dependent pancreaticadenocarcinoma in the form of immunization is provided against gastrinhormone in combination with one or more anti-cancer drugs.

BACKGROUND OF THE INVENTION

In 1998, approximately 29,000 people in the United States were diagnosedwith pancreatic adenocarcinoma, and approximately 28,900 people wereexpected to die from this tumor^([1]). The overall cure rate forpancreatic cancer remains less than 5% despite more than 20 years ofclinical trials. Only 10% of subjects have a potentially resectabletumor; however, even for subjects undergoing a curativepancreaticoduodenectomy, five-year survival is 6-24%^([2]). The vastmajority of subjects have unresectable tumors and develop metastaticdisease within the first year of therapy. The median survival forsubjects with metastatic disease is 3-6 months.

The description of cancertrophic agents set forth below includes bothgrowth factor and growth factor receptors which are surprisinglyexpressed or overexpressed in cancerous tumors or more specificallycancer cells.

Gastrin is highly expressed in the antral mucosa and duodenal bulb andexpressed at low levels in a variety of tissues, including the pancreas.Gastrin is also highly expressed in the fetal pancreas, a fact which maybe of significance in the development of pancreatic neoplasms^([3]).

The normal nonfetal pancreas shows no expression of gastrin isoforms orreceptor. It has been shown that a large percentage of patients withpancreatic cancer possess progastrin, glycine-extended gastrin, amidatedgastrin in their blood, and CCK-B/gastrin receptor are present in thetumor cells^([4]). Thus, it was later found that pancreaticadenocarcinoma expresses the precursor forms of gastrin, especially theprogastrin and glycine-extended forms. The tumor cells were alsodetermined to express the CCK-B/gastrin receptor. Similarly, theseprecursor gastrin forms and receptors were detected in other cancers,such as gastric, colonic, and hepatocellular carcinomas.

Several growth factors have been postulated to affect the growth anddevelopment of pancreatic cancer. Moreover, it is well recognized thatgastrin is a trophic hormone and promotes growth of gastrointestinal(GI) and non-gastrointestinal cancers^([4]). Gastrin has been shown topromote the growth of hepatocellular carcinoma, renal cell carcinoma,small cell carcinoma of the lung and also pancreatic carcinoma^([6-9]).Gastrin affects cell behavior in the form of circulating fully processedpeptides as well as autocrine process whereby incomplete processedprecursor gastrin, especially in the form of glycine-extended gastrincan stimulate cell growth or cell function^([10]).

In particular, a number of investigations have shown the important rolethat G17 gastrin and glycine-extended G17 (Gly-G17) gastrin play in theproliferation of gastrointestinal adenocarcinomas including pancreaticadenocarcinoma. It has been demonstrated that G17 gastrin causesproliferation of a variety of colorectal, gastric and pancreatic cancercell lines, both in vitro and in vivo^([11] [12] [6] [13]) and that anautocrine pathway may be involved ^([14] [15]). Gly-G17 gastrin has alsobeen shown to stimulate growth of various cancers via anautocrine/paracrine pathway^([16] [17]).

Gastrin is actually a family of peptides including G17 gastrin, G34gastrin, and the immature forms, glycine-extended G17 (Gly-G17) gastrinand glycine-extended G34 (Gly-G34) gastrin. G17 and G34 share a5-amino-acid carboxy-terminal sequence in common with cholecystokinin(CCK). It has been shown that in this sequence that interacts with theCCK-B/gastrin receptor^([11] [18]).

Gastrin requires post-translational carboxy-terminal alpha-amidationusing glycine as the amide donor. The penultimate intermediate isgastrin with a C-terminal glycine—the so-called glycine-extendedgastrins (Gly-G17 and Gly-G34). Similar concentrations ofglycine-extended forms and mature gastrins are often found. Gly-G17appears to have some of gastrin's biological activities^([17]).

Different tissues exhibit different patterns of post-translationalgastrin modification resulting in the accumulation of differentintermediates. While gastrin produced by the gastric antrum is largelyfully amidated G17^([19]), anterior pituitary corticotrophs almostentirely fail to process the amidation site, resulting in >99%glycine-extended gastrins. In neonatal pancreatic cells, gastrin islargely in the G34 form^([19]) and it is fully sulfated at Tyr29, aunique modification, making it CCK-like in its potency^([3]). Inneoplastic tissue, immature forms of gastrin typically predominate. Incolorectal carcinomas, a considerable amount of progastrin speciesaccumulates^([20] [21]). In rat pancreatic tumor AR42J, it has beenreported that only glycine-extended gastrins are present^([17]). Nothinghas been reported on the forms of gastrin produced by human pancreaticcancer cells.

The gastrin and CCK-B receptors were recently cloned and shown to beidentical^([22]). Messenger RNA for CCK-B receptors was detected in allpancreatic cancer cell lines of ductal origin and in normal pancreatictissue as well as in fresh tumor cells^([23] [24] [25]) and may beover-expressed in malignant pancreatic tissue in comparison with normaltissue^([26]). Some authors have detected CCK-B receptors usingradiolabeled ligand binding (either gastrin or CCK) technologies in bothnormal pancreas and tumor cell lines.^([27]) Others have failed todetect receptors in the tumor cell lines but do detect them in normaltissue^([28] [29]).

MacKenzie et al^([30]) demonstrated by radioligand-binding the abundantpresence of CCK-B/gastrin receptor on the rat pancreatic tumor cellline, AR42J. Tarasova et al^([31]) have shown that following ligandbinding assays, rapid clustering and internalization of theCCK-B/gastrin receptor occurred in the pancreatic tumor cell line AR42J,as well as in a variety of human gastric and colorectal tumor celllines. Incubation of the CCK-B/gastrin receptor with 1 nM of thespecific inhibitor CI-988 inhibited the proliferation ofgastrin-stimulated (1 nM) AR42J cells by about 47% after 96 hours oftreatment, which is consistent with competitive inhibition of thegastrin receptor^([32]). Anti-G17 antibodies have been shown to inhibitthe binding of gastrin to the CCK-B/gastrin receptors on the pancreatictumor cell line AR42J.

It has been shown that gastrin peptides increase the proliferation of GIcancer cell lines of human and animal origin both in vitro and invivo^([5]). More recent studies with four human pancreatic cell lineshave shown that all proliferation was increased by 40-68% G17 gastrinrelative to untreated controls. Studies with receptor antagonists showedthat this proliferative effect was mediated via the CCK-Breceptor^([11]). Other studies have reported similar results^([12]), butnot all studies report a positive effect even if the presence of CCK-Breceptors was confirmed by binding studies^([25]).

Additional studies compared the mitogenic effects of gastrin oncolorectal and gastric tumor cells obtained from cancer subjects atsurgical resection. It was shown that cells from 69% of gastric and 55%of colorectal tumors had an enhanced proliferation in response to G17gastrin, which was of greater magnitude than that seen in normal cellsobtained from the GI mucosa^([33] [34]).

It has been shown that the gastrin gene is activated in epithelial cellsderived from GI tumor specimens, but not in normal GI mucosal cells^([35] [36] [37] [21] [17][38]). Malignant epithelial cells have beenshown to produce mitogenic gastrin peptides, which can increaseself-proliferation of the surrounding cells, thereby inducing a state oftumor autonomy^([39] [16]).

Gastrin also stimulated in vivo tumor growth in mice inoculated withhuman Panc-1 cells. Tumor volume in mice treated with pentagastrin was127% greater than untreated control tumors, while those animalsreceiving a CCK-B receptor antagonist (without pentagastrin) had tumorsonly 60% as large as controls^([11]).

The stimulatory effect of gastrin was also demonstrated by antisense RNAdirected at gastrin^([40]) which suppressed the growth of humanpancreatic cell lines. The observation that gastrin mRNA is detectablein all normal as well as tumor cell lines and in fresh pancreatictissue, while gastrin peptide is detectable only in malignant tissue,suggested that gastrin mRNA may be translated only in the tumorcells^([15]).

Although inactive in stimulating acid secretion, Gly-G17 gastrin hasbeen shown to increase the proliferation of pancreatic^([41]) cancercells, G17 and Gly-G17 were found to be equipotent in stimulatingproliferation of rat pancreatic tumor AR42J cells.

The normal physiological functions of gastrin are mediated byCCK-B/gastrin receptors. Expression of the receptor occurs in all typesof gastrointestinal malignancies including colorectal, gastric,pancreatic, hepatoma,s and colorectal livermetastases^([42] [43] [24] [15] [44] [45] [46]). Different isoforms ofthe receptor exist^([51] [52]), and more than on CCK-B gastrin receptormay be co-expressed on individual cells. Therefore, antagonism of CCK-Breceptors may not be the optimal method to suppress the proliferativeaction of gastrin present either in the serum or produced locally by thetumor cells.

It has been shown that several types of tumors, e.g., colorectal,stomach, pancreatic and hepatocellular adenocarcinomas, possessCCK-B/gastrin receptors in their plasma membranes and that they respondto gastrin with powerful cellular proliferation^([53] [13]).Furthermore, more recently it has been discovered that many of thesecancer cells also secrete gastrin and thus effect an autonomousproliferative pathway^([21] [37] [16]).

The CCK-B/gastrin receptor belongs to a family of G protein-coupledreceptors with seven transmembrane domains with equal affinity for bothCCK and gastrin^([54]). This receptor was named a CCK type-B receptorbecause it was found predominantly in the brain^([55]). The receptor wassubsequently found to be identical to the peripheral CCK/gastrinreceptor in the parietal and ECL cells of the stomach^([56]). Thisreceptor has been well characterized in a number of normal^([57] [58])and tumor tissues^([59] [34]), and extensively studied using the ratpancreatic adenocarcinoma cell line AR42J^([60]). The AR42JCCK-B/gastrin receptor cDNA has been cloned and sequenced, and it ismore than 90% homologous in DNA sequence to the CCK-B/gastin receptor inrat and human brain, and more than 84% homologous in sequence to thecanine parietal cell CCK-B/gastrin receptor cDNA^([61]), demonstrating ahigh sequence homology even between species.

The peptide hormones G17 and G34 bind to the CCK-B/gastrin receptor onthe cell membrane of normal cells. However, it has been found that G17,and not G34, stimulates the growth of gastrin-dependent cancer cells.Serum-associated G17, in particular, has the potential to stimulate thegrowth of colorectal tumors in an endocrine manner mediated byCCK-B/gastin receptors^([34]) in the tumor cells. Gastrin-17 appears tobe particularly implicated in stimulating the growth of colorectaladenocarcinomas due to a possible increased affinity for theCCK-B/gastrin receptor on the tumor cells, over other gastrin hormonespecies^([62]). The CCK-B/gastin receptors were found to be expressed ina high affinity form on 56.7% of human primary colorectal tumors^([53]).It has been postulated that a potential autocrine loop may also existdue to endogenous production of precursor gastrin peptides by suchtumors^([21]). The resulting G17 ligand/receptor complex stimulates cellgrowth by way of secondary messengers for regulating cellfunction^([63]). The binding of G17 to the CCK- B/gastrin receptor leadsto activation of phosphatidyl inositol breakdown, protein kinase Cactivation with a resultant increase in intracellular calcium ionconcentration, as well as the induction of c-fos and c-jun genes viamitogen-activated protein kinase, which has been implicated in theregulation of cell proliferation^([64]). Additionally, gastrin bindingto the CCK-B/gastrin receptor has been associated with the subsequentincrease in phosphorylation by a tyrosine kinase, pp125FADK (focaladhesion kinase), which may also have a role in the transmission ofmitogenic signals^([65]).

A number of high affinity CCK-B/gastrin receptor antagonists have beenevaluated therapeutically both in vitro and in vivo in a number ofexperimental models of gastrointestinal cancer. For example, proglumide,a glutamic acid derivative^([16] [66] [67]) Benzotript, an N-acylderivative of tryptophan; L-365,260, a derivative of Aspercillin^([68]),and CI-988 a molecule that mimics the C-terminal pentapeptide sequenceof CCK^([69]) have been shown to effectively neutralize the effects ofexogenous gastrin on gastrointestinal tumor growth both in vitro and invivo^([6] [70]). However, these antagonists have severe toxic sideeffects and lack specificity as they block the action of all potentialligands of the receptor such as G34 and CCK in normal cells. Recently,highly potent and selective CCKB/gastrin receptor antagonists such asYM022^([71]) and YF476^([72]) have been also described.

Proglumide and Benzotript have been widely assessed in pre-clinicalstudies. The main problem with these compounds is their lack of potency,with relatively high concentrations required to displace G17. Despitethis, proglumide and benzotript inhibited the basal andgastrin-stimulated proliferation of a number of cell lines^([67]). Inaddition, proglumide increased the survival of xenograft mice bearingthe gastrin-sensitive mouse colon tumor, MC26 to 39 days in the treatedanimals from 25 days in the control animals.

Due to the low specificity of this class of gastrin antagonising agentsfor the gastrin/CCKB receptor, the inhibition of tumor growth may not beeffectively control with gastrin antagonists. Moreover, the cellularreceptors which recognize and bind the gastrins do not bind all theinhibitors tested^([16]). Thus, if complete inhibition of gastrinbinding to the receptor does not occur in the autocrine growth cascade,then the gastrin antagonists may be unable to block this mechanism oftumor growth promotion.

Recent developments have demonstrated the feasibility ofimmunoneutralization of hormones or their receptor moieties in order toinhibit the hormone controlled physiological functions or effects, suchas cellular growth. (U.S. Pat. Nos. 5,023,077 and 5,468,494)

For example, immunization with the immunogen G17DT elicits antibodiesthat react specifically with the aminoterminal end of G17 gastrin andGly-G17 gastrin (U.S. patent application Ser. No. 08/798,423). Theantibodies do not cross-react with any of the other gastrin speciestested, including G34 gastrin and CCK. Antibodies elicited by G17DTinhibit the binding of gastrin to the CCK-B/gastrin receptor on avariety of gastrointestinal tumor cellsi including pancreatic tumorcells. Antibodies elicited by G17DT inhibit the growth of human gastric,pancreatic, and colorectal cancer cells in vitro and in in vivo animalmodels of gastric and colorectal cancer. Immunological neutralizationhas been discovered to inhibit metastsis of colorectalcancer^([46] [47]).

The alternate or additional immunological weapon against the gastrineffect on pancreatic cancer growth comprises the induction ofanti-CCKB/gastrin receptor antibody binding with a specificanti-receptor GRE1 or GRE4 peptide epitope, as described in co-assignedpending U.S. patent application Ser. No. 09/076,372. Accordingly, thereceptor moieties can be prevented from binding the circulating gastrinhormone or fragments thereof. Furthermore, this immunological inhibitionof pancreatic cancer advantageously results in the internalization ofthe receptor antibody complex causing apoptosis-like cell death.

Certain anticancer chemical compounds have been found useful fortreating adenocarcinoma such as pancreatic tumors. For example,Gemcitabine (2′, 2′, difluorodeoxycytidine) is a nucleoside analog withstructural similarities to cytarabine. Its mode of action involvesdisruption of cell replication. Gemcitabine enters the cell via acarrier-mediated transport system that is shared with other nucleosides.It is phosphorylated sequentially to difluorodeoxycytidine monophosphate(diFdCMP), difluorodeoxycytidine diphosphate (diFdCDP) anddifluorodeoxycytidine triphosphate (diFdCTP). Preclinical studies ofgemcitabine have shown incorporation of the phosphorylated diFdCTP intoDNA^([73][74]).

Gemcitabine triphosphate is a substrate and competitive inhibitor of DNApolymerases alpha and epsilon. Once dFdCTP is incorporated into thegrowing chain, only one (or perhaps two) more nucleotide(s) can beincorporated, a novel mechanism termed “masked chain termination.” Onceadditional residues are incorporated at the 3′ end, gemcitabine cannotbe excised by the proofreading exonucleolytic activity of DNApolymerase^([48]). DNA fragmentation and apoptosis follow. As predictedby its mode of action, gemcitabine is active only in S-phase when cellsare actively replicating DNA^([49]).

Since pancreatic cancer has a high occurrence of metastasis, this methodalso omprises advantageous combination treatment with immunologicalanti-gastrin, anti-CCK-B/gastin receptor agents and chemotherapeuticagents such as irinotecan and optionally 5-FU/LV or gemcitabine, orboth.

Irinotecan is a chemotherapeutic drug (Camposar®), which has beenapproved for some types of cancer, mostly as second-live treatment. Ithas been applied in conjunction with 5-FU/LV against metastaticcolorectal carcinoma which progressed after 5-FU treatment.

Cisplatin is a drug used in a variety of neoplasms that is capable ofproducing inter-and intrastrand DNA cross-links. Cisplatin can beadministered alone or together with other chamotherapeucics.

In view of the very poor prognosis of pancreatic cancer and lack ofsignificant survival afforded by the currently available therapies, atherapeutic strategy involving immunological targeting of gastrin andits receptor in combination with chemotherapeutic methods using one ormore chemotherapeutic agents may provide a novel and efficacioustherapy.

SUMMARY OF THE INVENTION

Contrary to expectations, it has now been discovered that the immuneresponse to vaccination of the treated animal or human is notsignificantly repressed by chemotherapeutics, or at least can beovercome by adjusting the vaccine dosage.

Advantageously, therefore, the present invention provides a treatment ofpancreatic cancer comprising combining immunotherapy with one or morethan one anticancer growth active immunogen and chemotherapy wherein thechemotherapy comprises one or more chemotherapeutic anticancer agent.

The invention provides a combination of methods for use in the treatmentof pancreatic cancer including metastatic tumors thereof, wherein theimmunotherapy is administered both in the form of an active or passiveimmunological composition comprising one or more cancer trophic targetand the chemotherapy comprise one or more chemotherapeutic agentsuitable for the inhibition of cancer growth. In the general context ofthis invention, the active immunization comprises an anti-growth factorimmunogen and/or an anti-growth factor receptor immunogen, and thepassive immunization comprises anti-growth factor antibodies, andanti-growth factor receptor antibodies which are polyclonal ormonoclonal.

In particular, the combination of methods provides treatment ofpancreatic cancer by immunological therapy directed against hormones andreceptors thereof which stimulate the growth of pancreatic cancer cells,and concomitantly by administration of pharmaceutically acceptablechemotherapeutic agents.

The invention also provides a combination of treatment of pancreaticcancer comprising administering an immunogenic composition containing aconjugate of the amino-terminal G17 peptide epitope covalently linked toan immunogenic carrier proteins and a chemotherapeutic composition.

One form of active immunization according to the invention provides anantigastrin effective immunogenic composition comprising an epitope ofthe gastrin peptide G17 which is covalently linked through a spacerpeptide to an immunogenic carrier or immunogenic carrier fragment.

More particularly, the invention may provide a conjugate of theaminoterminal G17 peptide epitope linked to a seven amino acid peptidespacer, the spacer being attached to an ε-amino acid carrying side chainof the lysine residue of diphtheria toxoid and a chemotherapeuticcomposition carrier protein .

The immunogenic composition according to this invention contains andosage in units ranging from approximately 10 μg to 5000 μg ofimmunogen.

An alternate embodiment of the invention provides an anti-gastrinreceptor immunogen. For example, such an embodiment provides animmunogen which comprises a CCKB/gastrin receptor peptide or fragmentthereof which elicits antibodies in the immunized patient, wherein theantibodies are specifically directed against an epitope of the receptorso as to bind and inactivate the receptor.

The antibodies produced by the anti-CCK-B/gastrin receptor immunogensthereby inhibit the growth stimulatory pathway, including the autocrinegrowth-stimulatory pathway of tumor cells and ultimately the growth ofthe tumor.

Another embodiment of the invention provides an immunogen which elicitsan auto-antibody specifically directed to a gastrin receptor, such thatupon binding the antibody is internalized into the receptor associatedpancreatic tumor cell.

A further embodiment of the invention provides for an immunogen whichelicits an antibody specifically directed to the gastrin receptor, orfragment thereof, such that upon binding the antibody is internalizedinto the nucleus of the receptor associated pancreatic tumor cell.

An embodiment of the treatment of pancreatic cancer providesimmunization with an anti-CCKB/gastrin receptor immunogen, alone/orcombined with treatment for the cancer by administering a compositioncomprising one, or more than one, chemotherapeutic agent effectiveagainst pancreatic cancer.

A further embodiment of the invention advantageously provides animmunogenic composition formulated as a water-in-oil emulsion amenablefor intramuscular injection.

Another embodiment of the treatment of pancreatic cancer providesimmunization with both anti-gastrin immunogen and anti-gastrin receptorimmunogen combined with one, or more than one, chemotherapeutic agent.

The treatment according to the invention combines the immunologicalphase of therapy with one or more chemical adjuvant compounds selectedfrom known pharmaceutically acceptable taxanes, such as e.g. docetaxel,taxotere, Paclitaxel, 7-Epi-Taxol, 10-Deacetyl Taxol, as well asmixtures thereof, 5-fluorouracil (5-FU), cisplatin, gemcitabine,irinotecan (also called Camposar® or CPT-11), and tamoxifen 5-FU may beadministered with leucovorin.

The chemotherapy comprises doses of 5-FU ranging from 50 to 1000mg/m²/d, with leucovorin at 90 mg/d to 100 mg/d or irinotecan rangingfrom 200-300 mg/m²/d, gemcitabine ranging from 100-1500 mg/m²/d;cisplatin (platinol) ranging from 40 mg- 100 mg/m²/d; and tamoxifen from10 mg-20 mg tablet per day. For example, combinations ofchemotherapeutic agents comprise 5-FU Cisplatin, 5-FU-Gemcitabine or5-FU with leucovorin & cisplatin.

The invention provides a treatment of G17DT immunogen (100-500 μ) incombination with gemcitabine of unresectable metastatic carcinoma of thepancreas in previously untreated subjects.

In accordance with this invention, the method of treatment of pancreaticcancer provides periodic administration of immunological anti-growthstimulating agents in conjunction with a chemotherapeutic agentcomprising one or more chemical compounds having an anti-cancer effect.The immunological agents are either hormone immunogens for activeirmmunization or passive immunization with exogenous anti-growth factorantibodies. The exogenous human antibodies can be produced in transgenicanimals or other suitable subjects using standard techniques. Forpassive immunization, the antibodies can be monoclonal, polyclonal or ahybrid. The antibodies are administered in purified form, such as, e.g.IgG fractions, comprising dosages sufficient to neutralize thecirculating growth factors or hormones, e.g., gastrin G17 or Gly-G17, ortheir receptors.

A further growth factor or hormone specific embodiment of the inventionutilizes the exogenously added anti- CCKB/gastrin receptor antibody inmodified form with agents such as toxins, or radiolabelled substances.The toxin can be of the cholera type. The radiolabel can be ¹²⁵Iodine,¹³¹Iodine, ¹⁸⁷Rhenium or ⁹⁰Yttrium.

For example, the embodiment provides a radiolabelled specificanti-cancertrophic antibody to destroy the cell upon internalizationfurther in combination with other chemotherapeutic and otherimmunologically active agents.

Radiolabeled antibodies can also be used for detection diagnoses whereinthe radiolabel comprises ¹²⁵Iodine, ¹³¹Iodine, Technetium (T_(c)),¹¹¹Indium, ⁶⁷Gallium, or ⁹⁰Yttrium.

DETAILED DESCRIPTION OF THE INVENTION

Anti-G17DT antibodies administered in animals with xenotransplants ofvarious cancers, as well as antibodies elicited by active immunizationof subjects with colorectal or stomach cancer with G17DT conjugate,bound both G17 and Gly-G17 gastrins at high affinity. Furthermore,safety and dose ranging studies in subjects with advanced colorectal,stomach, and pancreatic cancers have demonstrated that high-affinityantibodies are elicited by G17DT immunogen. Biological therapies such asimmunization with G17DT in combination with chemotherapy may show ahigher degree of efficacy than each alone. The higher efficacy is dut tothe inhibition of a proliferative factor such as gastrin, is cytostatic,and the chemotherapy is a cytotoxic effect. A combination of the twomodalities is synergistic, similarly as previously demonstrated withanti-HER2 antibody treatment in combination with chemotherapy inadvanced breast cancer^([75]) and which, more specifically, is shown byresults of pre-clinical studies of combinations of G17DT withchemotherapeutic agents.

The majority of neutralizing antisera raised against gastrin peptideshas been directed against the 5-amino-acid carboxy-terminal portion ofthe molecule common to G17 gastrin (SEQ ID NO: 4), G34 gastrin (SEQ IDNO: 5), and cholecystokinin (CCK). This carboxy-terminal sequence ofthese peptide hormones interacts with the CCK-B/gastrin receptor^([14]). G17DT conjugate was developed in an attempt to generateantibodies against the amino-terminal end of G17 and Gly-G17 gastrins.G17DT conjugate is constructed from a synthetic 16-residue peptidecomprising an epitope derived from the amino acid residue 1-9 of G17gastrin linked at the C-terminal to a 7 amino acid residue spacerpeptide terminating in a cysteinyl residue. The peptide is cross-linkedvia its C-terminal cysteine residue to a carrier protein, Diphtheriatoxoid (DT), using the bifunctional cross-linker EMCS to form the G17DTconjugate. G17DT has been formulated in a water-in-oil emulsion suitablefor intramuscular injection.

Other immunogens for use in the invention are disclosed in thecoassigned U.S. Pat. Nos. 5,023,077, 5,488,494; 5,607,676, 5,866,128;5,609,870; 5,688,506, and 5,662,702 which are incorporated herein byreference in their entirety.

It has been shown that G17-specific antibodies raised, for example,against the instant G17DT immunogen were affinity-purified from rabbitserum and tested for their ability to inhibit in vitro the binding ofradioiodinated human G17 to AR42J cells, a rat pancreatic cancer cellline that expresses gastrin receptors. It was shown that the anti-G17antibodies, pre-mixed with the labeled G17, significantly (>90%)inhibited the binding of G17 to the cells. This data demonstrate theircapacity of the antibodies to neutralize the biological activity ofhuman G17 in pancreatic cancer cells.

G17DT does not cause significant systemic side effects, and no evidencehas been found for deleterious effects of long-term neutralization ofG17 gastrin and Gly-G17 gastrins. The only significant side effectfollowing immunization-with G17DT is injection site reactions.

Neutralization of the endocrine and autocrine/paracrine effects of G17and glycine-extended G17 gastrin is proposed as a mechanism by whichG17DT immunization can reduce gastrin-stimulated tumor growth. andincrease survival of the patient. A G17DT formulation has been developedthat elicits an immune response while exhibiting an acceptable localreactogenicity.

Furthermore, as described in the co-assigned international patentapplication serial number PCT/US99/10750, anti-gastrin immunizationtreatment combined with lower than normal amounts of Leucovorin/5-FU,has been advantageously effective.

The methods of the invention are directed to the treatment of gastrinhormone-dependent tumors in animals, including humans, and compriseadministering to a patient an anti-CCK-B/Gastrin-receptor immunogen,which induces the formation of antibodies in the immunized patient whichbind to the CCK-B/gastrin-receptor on the tumor cells. Antibodies boudnto the cell receptors block the binding of the hormone to the receptorand thereby inhibit the growth promoting effects of the hormone. Moreimportantly the receptor/anti GRE1 (anti-gastrin receptor epitope 1)antibody complex is rapidly internalized, traverses the cytoplasm andenters the nucleus. The complex one in the nucleus triggers the affectedtumor cells to commit suicide (apoptosis).

The immunogens of the invention comprise natural or synthetic peptidesof the human CCK-B/gastrin-receptor which act as immunomimics. Inparticular, two synthetic peptides have been developed as theimmunomimics. These peptides, developed from the amino acid sequence ofthe CCK-B/gastrin-receptor, are immunogenic and cross-reactive with theendogenous CCK-B/gastrin-receptor of tumor cells both in vivo and invitro. Peptide 1 consists of amino acids 5 through 21 of the CCK-B/gastrin-receptor sequence KLNRSVQGTGPGPGASL (Peptide 1, SEQ ID NO.: 1in the Sequence Listing). Peptide 1 constitutes part of theamino-terminal domain of the receptor and is located on theextracellular surface of the cell membrane.

In another embodiment, the immunogen comprises Peptide 4, which consistsof the amino acid sequence of the CCK-B/gastrin-receptor:GPGAHRALSGAPISF (Peptide 4, SEQ ID NO.: 2 in the Sequence Listing).Peptide 4 is part of the fourth extracellular domain of the receptor andit too is on the outer side of the cell membrane.

The immunogens may also comprise an extension or spacer peptide suitablefor projecting the immunomimic peptide away from the protein carrier andto enhance its capacity to bind the lymphocyte receptors. A suitablespacer peptide has the amino acid sequence SSPPPPC (Serine (Ser) spacer,SEQ ID NO.:3 in the Sequence Listing). However, other spacer peptideswould be suitable as well. The immunomimic peptides, with or without thespacer, are then conjugated to a protein carrier, such as Diphtheriatoxoid, via a cysteine residue at the carboxy terminal end. The spacerpeptides are not immunologically related to theCCK-B/gastrin-receptor-derived peptides and should therefore enhance,but not determine, the specific immunogenicity of the receptor-derivedpeptides.

The presence and density of CCK-B/gastrin-receptors on tumor cells in apatient can be determined in vitro by reacting labeled anti-receptorantibodies with a sample of obtained from a tumor biopsy. Theanti-receptor antibodies can be labeled with either a radioactivetracer, a dye, an enzyme or a fluorescent label, as known in the art. Inaddition, the responsiveness of the tumor cells to gastrin can beevaluated in vitro from a tumor biopsy sample of the patient usingstandard techniques. Patients having tumor biopsy samples positive forthe CCK-B/gastrin-receptor antibody assay are typical candidates fortreatment by the methods of the invention.

An effective dosage ranging from 0.001 to 5 mg of the immunogeniccomposition is administered to the patient for the treatment of thegastrointestinal cancer. The effective dosage of the immunogeniccomposition should-be capable of eliciting an immune response in apatient consisting of effective levels of antibody titer against theCCK-B/gastrin-receptor 1-3 months after immunization. Following theimmunization of a patient, the effectiveness of the immunogens ismonitored by standard clinical procedures, such as ultrasound andmagnetic resonance imaging (MRI), to detect the presence and size oftumors. The antibody titer levels against the receptor may also bemonitored from a sample of blood taken from the patient. Boosterimmunizations are given as required to maintain an effective antibodytiter. Effective treatment of gastrin-dependent cancers, such asstomach, liver, pancreatic and colorectal adenocarcinomas, according tothis method should result in inhibition of tumor growth and a decreasein size of the tumor.

The antibodies raised by the anti-CCK-B/gastrin-receptor immunogens ofthe present invention may have anti-trophic effects againstgastrin-dependent tumors by three potential mechanisms: (i) inhibitionof gastrin binding to its receptor, (ii) degradation or disruption ofthe signal transduction pathway of tumor cell proliferation; and (iii)induction of apoptosis (or cell suicide) in cells wherereceptor/antibody complexes are internalized and migrate into thenucleus.

In another embodiment of the invention, anti-CCK-B/gastrin-receptorantibodies are administered to a patient possessing aCCK-B/gastrin-receptor-responsive tumor. The antibodies specificallybind to the CCK-B/gastrin-receptors on the tumor cells. The binding ofthe antibodies to the receptors prevents the binding of gastrin to itsligand in the membranes of cells and, therefore, the growth signal forthe gastrin-dependent tumor cells is inhibited and the growth of thetumor is arrested. The antibodies are preferably chimeric or humanizedantibodies, or fragments thereof, which effectively bind to the targetreceptor and may be produced by standard techniques, such as, e.g.,those disclosed in U.S. Pat. Nos. 5,023,077, 5,468,494, 5,607,676,5,609,870, 5,688,506 and 5,662,702. These exogenously producedantibodies may also be useful for killing tumor cells that bear theCCK-B/gastrin-receptor on their plasina membranes by virtue of theirinhibiting the growth of the tumor cells or delivering a toxic substanceto the tumor cell. Therapeutic anti-CCK-B/gastrin.antibodies are thosereactive with extracellular domains 1 and 4 of the receptor protein asGRE-1 and GRE-4, respectively. The inhibition of tumor growth in thismethod of immunization is also monitored by ultrasound imaging and MRIand repeated immunizations are administered as required by the patient.

The effectiveness of the antibodies in inhibiting tumor cell growth andkilling of tumor cells can be enhanced by conjugating cytotoxicmolecules to the anti-CCK-B/gastrin antibodies and the anti-gastrin G17or G17-gly antibodies. The cytotoxic molecules are toxins, for example,cholera toxin, ricin, (α-amanitin, or radioactive molecules labeled, forexample, with ¹²⁵I or ¹³¹I, or chemotherapeutic agents, as for example,cytosine arabinoside or 5-fluorouridine (5-FU).

In addition to antibodies radiolabeled with ¹²⁵I and ¹³¹I theanti-CCK-B/Gastrin-receptor antibodies can also be labeled withradionuclides such as ¹¹¹ Indium and ⁹⁰Yttrium. In this aspect of theinvention, the antibodies are useful for the detection and diagnosing ofCCK-B/gastrin-receptor possessing tumors in vivo, by administering theseantibodies to the patient, and detecting bound antibodies onCCK-B/gastrin-receptor-containing tumor cells. After allowing the radiolabeled anti-CCK-B/gastrin antibodies to reach the tumor, about 1-2hours after injection, the radioactive, “hot spots” are imaged usingstandard scintigraphic procedures as previously disclosed (Harrison'sPrinciples of Internal Medicine, Isselbacher et al. eds. 13 _(th) Ed.1994).

The compositions in which the immunogens are administered for thetreatment of gastrin-dependent tumors in patients may be in a variety offorms. These include, for example, solid, semi-solid and liquid dosageforms, such as tablets, powders, liquid solutions, suspensions,suppositories, and injectable and infusible solutions. The preferredform depends on the intended mode of administration and therapeuticapplications. The compositions comprise the present immunogens andsuitable pharmaceutically acceptable components, and may include othermedicinal agents, carriers, adjuvants, excipients, etc. Suitableadjuvants may include nor-muramyl dipeptide (nor-MDP, Peninsula Labs.,CA), and oils such as Montanide ISA 703 (Seppic, Inc., Paris, France),which can be mixed using standard procedures. Preferably, thecompositions are in the form of a unit dose. The amount of activecompound administered for immunization or as a medicament at one time,or over a period of time, will depend on the subject being treated, themanner and form of administration, and the judgment of the treatingphysician.

The anti-CCK-B/gastrin-receptor antibodies of the invention for passiveimmunization can be administered to a patient intravenously using apharmaceutically acceptable carrier, such as a saline solution, forexample, phosphate-buffered saline.

The pharmacology and toxicology for the instant combined treatment ofadvanced pancreatic cancer is described below:

EXAMPLE A

G17DT was administered to 28 patients with advanced pancreaticadenocarcinoma at weeks 0,1 and 3 at a 250 μg dose^([16]). Only onepatient failed to mount an antibody response. G17DT was well toleratedwith no systemic side effects. One patient developed a sterile abscessthat settled following aspiration. Survival was found to besignificantly improved in G17DT patients when compared to an historicalcontrol matched in terms of age, stage and co-existing morbidity byPOSSUM scoring^([40]).

Concerning the response rates of subjects with pancreatic cancer themedian time to onset of the immune response to G17DT appears to be doserelated and to be optimal at ≧250 μg G17DT.

EXAMPLE B

The immuno-electronmicroscopy studies used an antiserum directed againstthe amino-terminal end of the CCK-B/gastrin-receptor (GRE-1 epitope)show that after one hour incubation, the distribution ofimmunogold-label CCK-B/gastrin-receptor antibody was quicklyinternalized as 12% of the antibody receptor complex was associated withthe cell membrane, 36.6% within the cytoplasm, 7.9% in the nuclearmembrane and, quite surprisingly, 43.5% within the cell nucleus. Areasof intense CCK- B/gastrin-receptor immunoreactivity within the nucleuswere found on chromatin, which may suggest specific binding sites forregulation of the DNA.

These electron microscopy studies with anti-immunoglobulin conjugated togold beads (immmunogold) reveal that an extremely rapid turnover of theanti-receptor/receptor complex occurs in the tumor cells; as early as 10seconds after exposure to antibodies, complexes are detectable in thecell nucleus.

EXAMPLE C Immunological Efficacy

Patients' sera were assessed for antibodies to G17 gastrin at 2-4 weeklyintervals. Anti-gastrin-17 antibodies were measured using a titrationand inhibition radioimmunoassay with ¹²⁵I labeled human gastrin-17.Assays for antibodies to G17 gastrin in the pancreatic cancer trials 1and 2 have been performed by a G17 antigen-based ELISA.

The pharmacodynamics of the immune response to G17DT was evaluated as afunction of the dose and treatment regimen for G17DT. The frequency ofseroconversion and time to onset of production of G17 gastrin-specificantibodies was used to estimate the optimal dose.

A positive immune response in test serum by RIA was defined as being ≧40fold above non-specific background determined on a 1:40 dilution ofpre-immune subject serum within the first 12 weeks post-immunization.This corresponds to approximately 10% of total ¹²⁵I G17 cpm added in theRIA assay. A positive response in the ELISA assay approximates ≧4 unitsin the ELISA assay which is comparable to that observed by RIA.

To facilitate comparison of doses and formulations, the immune responseup to and including the 12-week time point observed in subjects withnon-resectable, locally advanced (stage II/III) and metastatic (stageIV) pancreatic cancer were used to determine the proportion of immuneresponders among the treatment groups in the various studies. Theproportion of immune responders and the median time to develop an immuneresponse are summarized in Tables A and B, respectively.

A dose finding phase II study of G17DT in 22 patients with pancreaticcarcinoma demonstrated greater survival in patients who mounted anadequate antibody response when compared to non-responders (7.89 versus4.93 months)^([39]). TABLE A Immune response in subjects with StageII-IV pancreatic cancer Studies 1&2 Study (Stage II-IV) G17DT DoseSchedule n N^(a,b) %  10 μg 0, 4, 8 wk — — —  10 μg 0, 2, 6 wk — — — 100μg 0, 4, 8 wk — — — 100 μg 0, 2, 6 wk 5 13 38 165 μg 0, 4, 8 wk — — —250 μg 0, 4, 8 wk — — — 250 μg 0, 2, 6 wk 6 10 60 250 μg 0, 1, 3 wk — —— 330 μg 0, 4, 8 wk — — — 330 μg 0, 2, 6 wk — — — 330 μg 0, 2, 10 wk  —— — 495 μg 0, 4, 8 wk — — — 990 μg 0, 4, 8 wk — — — Total 11  23 48n = number of subjects with an immune response.N = number of subjects (immune responders and non-responders) that havecompleted 12 weeks% = (n/N) × 100^(a)In study 1, 4 subjects have not completed 12 weeks (evaluationongoing).^(d)In study 2, 11 subjects have not completed 12 weeks (evaluationongoing); no immune response data available.

TABLE B Time to immune response in subjects with Stage II-IV pancreaticcancer 1^(a) & 2^(b) Study (Stage II-IV) G17DT Dose Schedule Median(weeks) ± SD  10 μg 0, 4, 8 wk —  10 μg 0, 2, 6 wk — 100 μg 0, 4, 8 wk —100 μg 0, 2, 6 wk 10 ± 1  165 μg 0, 4, 8 wk — 250 μg 0, 4, 8 wk — 250 μg0, 2, 6 wk 6 ± 3 250 μg 0, 1, 3 wk — 330 μg 0, 4, 8 wk — 330 μg 0, 2, 6wk — 330 μg 0, 2, 10 wk  — 495 μg 0, 4, 8 wk — 500 μg 0, 4, 8 wk — 990μg 0, 4, 8 wk — Mean — 8 ± 2^(a)In study 1, 4 subjects have not completed 12 weeks (evaluationongoing).^(b)In study 2, 11 subjects have not completed 12 weeks (evaluationongoing); no immune response data available.Chemotherapy

EXAMPLE 1 Activity of Gemcitabine

The US FDA approved gemcitabine for use in pancreatic cancer based onthe results from several clinical trials [Gemzar® (gemcitabine HCl)package insert, 1996, 1998, summarized in Table 3]. Subjects withlocally advanced or metastatic disease were treated with gemcitabine1000 mg/m² weekly×7, or ×3, followed by one week of rest, then weekly ×3every four weeks thereafter. Early Phase II trials indicated that asignificant number of subjects experienced some palliation of symptomsdespite only modest objective response rates. To quantitate theseeffects, a novel end point termed Clinical Benefit Response wasdeveloped for use in subsequent trials.

Clinical Benefit Response is a composite of degrees of pain (analgesicconsumption and pain intensity), Kamofsky performance status, and weightchange. Gemcitabine was the first agent to be approved using clinicalbenefit response as an endpoint. Clinical benefit required a sustained(≧4 weeks) improvement in at least one parameter without worsening inany others. Subjects were considered clinical benefit responders only ifthey showed at least a 50% reduction in the level of pain (Memorial PainAssessment Card) or consumption of pain medication, or at least a20-point improvement in performance status (Karnofsky Performance Scale)for a period of at least four consecutive weeks, without showing anysustained worsening in any of the other parameters. A subject was alsoconsidered a clinical benefit positive responder if stable in all theseparameters.

EXAMPLE 2 Therapy with Gemcitabine

Prior to the approval of gemcitabine (Gemzar®, Eli Lilly & Co.) in 1996for the first-line treatment of locally advanced and metastaticadenocarcinoma ofthe pancreas, 5-fluorouracil (5-FU) had been thestandard of GI or pancreatic cancer care for 30 years. A review ^([50])of 28 Phase II trials involving 25 new agents showed that none providedany improvement over 5-FU in subject outcome, with a median objectiveresponse rate of 0% (range 0-14%) and a median survival of 3 months(range 2-8.3 months). Suggestions that combined chemotherapeutictreatments offered improvements over 5-FU alone were not confirmed inrandomized Phase III trials^([50]).

Gemcitabine exhibits several self-potentiation mechanisms which enhanceits incorporation into DNA^([76]). These effects are mediated viainteractions of gemcitabine and its metabolites with the enzymes ofpyrimidine nucleotide metabolism and are believed to be significant inproducing the high concentration of active drug in cells and inprolonging the half-life of active drug in cells. These include thefollowing:

Gemcitabine triphosphate directly inhibits dCMP deaminase, thusinhibiting the breakdown of gemcitabine monophosphate todifluorodeoxyuridine monophosphate (the major breakdown pathway)

Gemcitabine triphosphate may also inhibit CTP synthase, which catalyzesthe synthesis of CTP from UTP and ammonia (or glutamate), additionallydepleting dCTP pools.

Inhibition of ribonucleotide reductase by gemcitabine diphosphatereduces the concentrations of dCTP and dCDP, both of which feedbackinhibit deoxycytidine kinase. Thus, more gemcitabine is phosphorylatedbecause the feedback inhibition is removed.

Gemcitabine has also been shown to be a potent radiosensitizer. Thisactivity does not parallel the incorporation of the phosphorylated druginto DNA. Rather, it paralleles the intracellular depletion of dATP,suggesting that the inhibition of ribonucleotide reductase is the keymechanism of this action^([73] [74] [1]). In general, agents (e.g. urea)that reduce dNTP pools act as radiation sensitizers. The intermediatediFdCDP (gemcitabine diphosphate) is a potent inhibitor ofribonucleotide reductase. This inhibition causes a decrease in all fourdeoxynucleotide triphosphate intracellular pools, which results in aninhibition of DNA synthesis. Variation in the extent of depletion ofeach dNTP pool in different cell types suggests that the greaterdepletion of the dATP pool in particular observed in solid tumor celltypes may account for the greater clinical activity of gemcitabine insolid tumors^([74] [1]).

Gemcitabine rapidly distributes into total body water after IVadministration. The volume of distribution is affected by duration ofinfusion, age, and sex. Longer infusions result in higherconcentrations.

Clearance is independent of dose and duration of infusion but isvariable, and is influenced by age. Because the volume of distributionincreases with longer infusion times, its elimination half-life islonger when it is infused over a longer period.

Gemcitabine is deaminated by cytidine deaminase in plasma todiflurodeoxyuridine, which is inactive. Only 5% is excreted unchanged asgemcitabine.

Gemcitabine is generally less well tolerated than 5-FU, but despite ahigher incidence of adverse events, its overall toxicity is consideredmoderate. There is no evidence of cumulative toxicity.

A treatment of the invention combines immunoneutralization of G17gastrin or G17-Gly gastrin with the chemotherapy with gemcitabine. Theadvantageous aspect of this combination affords a lower dosage ofgemcitabine or irinotecan (or some similarly amenable and approvedanti-cancer drug) such that the toxicity and other adverse side effectsare reduced. In addition, the immunization with, e.g., G17-DT immunogencontaining compositions, can be administered at a time preceding thechemotherapy in order to avoid suppressing of the immuno response beforea sufficient titer of auto-antisera has been raised in the treatedsubject.

EXAMPLE 3 Therapy with Irinotecan

Irinotecan injection (irinotecan hydrochloride injection) is asemisynthetic derivative of camptothecin, an alkaloid extract fromplants such as Camptotheca acuminata. The chemical name is(S)-4,1-diethyl-3,4,12,14-tetrahydro-4-hydroxy-3,14-dioxi-[H-pyrano[3′,4′:67]-indolizino[1,2-b]quinolin-9-yl-[1,4′-bipiperidine]-1′-carboxylate,monohydrochloride, trihydrate. It is supplied as a sterile, pale yellow,clear, aqueous solution. Each milliliter of solution contains 20 mgirinotecan. (The Camptosar package insert provides detailed labelinginformation for irinotecan). Irinotecan is an emetogenic. Thereforepatients may receive premedication with antiemetic agents. Irinotecantherapy had been shown to cause GI adverse effects, in particular earlyand late diarrhea. Early diarrhea may be accompanied by cholinergicsymptoms. Prophylactic or therapeutic administration of atropine shouldbe considered in patients experiencing cholinergic symptoms. Latediarrhea should be promptly treated with loperamide. In addition to theGI manifestations, irinotecan has been shown to cause myelosuppresionand hypersensitivity reactions. Only patients with adequate hematologic,renal, and hepatic function, as well as patients with nocontraindication to irinotecan from previous irinotecan-based therapy,are able to avoid or immunize the frequency and severity of toxiceffects such as neutropenia and GI abnormalities.

Patients are permitted to remain on the medications they are takingexcept for immunosuppressants, including systemic (i.e., oral orinjected) corticosteroids. All concomitant medications should berecorded on the appropriate page of the CRF.

Palliative radiotherapy is allowed. In the event that gemcitabinetherapy is terminated because of a SAE, G17DT immunization can becontinued.

EXAMPLE 4 Therapy with Cisplatin

Injections with Platinol, a solution of cisplatin or cis-diamminedichloroplatinual II, is used mostly in combination with other cytotoxicagents has used as a potential cure of testicular germ cell neoplasms.Substantial activity has been observed in the treatment of small celllung cancer, bladder cancer and ovarian germ cell tumors. According tothe invention, cisplatin may augment antipancreatic cancer treatment incombination with other pharmaceutically acceptable cytitoxic agents andimmunogens or exogenous application of anti-cancertroph antibodies.Suitable effective dosing may range as high as 1000 mg/m² per weekalthough the chemotherapeutic effect may be enhanced with simultaneousimmunotherapy so as to allow lower chemotherapeutic dosages.

EXAMPLE 5 Effect of Gemcitabine on G17DT Immunogenicity

The example depicts an in vivo test to assess the effect of thechemotherapeutic agent Gemcitabine on the immunogenicity of the G17DTimmunogen. For that purpose, as a model animal system, mice wereimmunized intraperitoncally (IP) with 125, 250 and 500 μg doses of G17DTin Montanide ISA 703 emulsions of 0.1 ml volume on days 0, 28 and 56.Gemcitabine was given intravenously (IV) at a dose of 21.4 mg/kg in avolume of 0.2 ml on days 0, 7, 14, 21, 28, 35, 42, 56, 63 and 70.Control mice received saline vehicle without the chemotherapeutics. Theresultant anti-G17 antibody responses were measured by ELISA in seracollected every two weeks, and one bleed at day 21, over the course ofthe study.

The G17DT immunogen was formulated under sterile conditions using PBS(physiological saline solution) as diluent. The emulsion was produced bymixing the agueous phases of immunogens with Montanide ISA 703 at anoil: agueous phase w/w ratio of 70:30.

Aliquots 8-10 mg dry Gemcitabine were weighed to be solubilized in PBSat a human treatment concentration of 3.424 mg/ml Gemcitabine beforei.v. administration.

The results of the treatment over the course of 84 days showed that allmice responded to G17DT immunogen with similar kinetics comparing themedian responses of all groups. (see Table 1).

Mice immunized with 125 μg G17DT manifested a statistical decrease inmean anti-G17 titers when concomitantly treated with Gemcitabine.However, the suppression was overcome by increasing the dose ofimmunogen to 250 μg or 500 μg G17DT.

This second part of the example depicts cell proliferation of humanpancreatic cell lines, PANC-1, BxPC3 and PAN-1 using a tetrazolium-basedcombined with anti-gastrin G17 antibodies induced by G17DT (10-500μg/ml). The G17DT elicited antibodies are active against bothserum-associated and tumor-secreted, proliferative forms of gastrin. ThePAN-1 cell were administered at clinically reflective doses.

G17DT concentrations of 100 and 50 μg/ml increased the in vitroinhibitory effects of Gemcitabine (1.0-0.01 μg/ml) by 11-38% (p<0.05,ANOVA) when compared to the individual agents for all three cell lines.

In vivo G17DT alone inhibited basal pancreatic tumor weight by 33%(p=0.016, ANOVA) compared to 38% for Gemcitabine (p=0.004, ANOVA). Whencombined the agents inhibited tumor weight by 55% which was significantfrom G17DT alone (p=0.025). Thus the immunological agent G17DT maypromote the therapeutic efficacy of Gemcitabine. TABLE 1 Mean Anti-G17Titer ± Standard Error Plus Student's t-Test DAY OF STUDY 0 14 21 28 4256 70 84 Group 1; 125 μg 0 1.006 ± 240 1.132 ± 140 1.227 ± 210   74.780± 7.655  40.200 ± 4.883 241.140 ± 37.905 95.940 ± 23.248 G17DT PlaceboTreatment Group 2, 125 μg 0  292 ± 59  408 ± 77 408 ± 104 43.860 ±11.118 21.497 ± 6.813  64.200 ± 18.788 37.774 ± 9.480  G17DT GemcitabineTreatment t-test Group 1  0.020¹ 0.002¹  0.008¹  0.051¹  0.054¹ 0.003¹ 0.049¹ vs. 2 P(T <= t) two-tail Group 3; 250 μg 0 2.047 ± 717 2.074 ±575 2.349 ± 622   86.840 ± 34.076 25.913 ± 8.730  71.788 ± 21.755 42.166± 13.013 G17DT. Placebo Treatment Group 4; 250 μg 0   923 ± 242 1.899 ±724 2.863 ± 1.284 169.300 ± 65.955   40.620 ± 11.494 256.560 ± 59.74373.220 ± 17.674 G17DT. Placebo Treatment t-test Group 3 0.176 0.855 0.728 0.299 0.338 0.020¹ 0.195 vs. 4 P(T <= t) two-tail Group 5; 500 μg0 1.555 ± 160 4.703 ± 963 6.489 ± 1.545 107.398 ± 26.096   43.146 ±13.699 196.000 ± 44.006 118.667 ± 50.824  G17DT. Placebo Treatment Group6; 500 μg 0 1.100 ± 452 1.715 ± 790 4.372 ± 2.127 653.925 ± 360.669162.900 ± 90.679 166.800 ± 87.853 77.450 ± 13.846 G17DT. PlaceboTreatment t-test Group 5 0.370 0.043¹ 0.436 0.130 0.184 0.760  0.407 vs.6 P(T <= t) two-tail¹Statistical significance at p ≦ 0.05

Another embodiment of the present invention provides treatment with morethan one chemotherapeutic agent in combination with active immunizationagainst an appropriate growth factor and/or growth factor receptor. Forexample, such treatment can involve a combination of 5-FU/Leucovorin or5-FU plus cisplatinum.

As a preclinical experiment, mice were treated with a combination of thetwo anticancer agents 5-FU and Cisplatinum and tested as to the extentof numerous suppressive effects.

EXAMPLE 6 Effect of 5-FU & Cisplatinum on G17DT Immunojenicity

This example concerns the effect of co-treatment with thechemotherapeutic agent 5-fluorouracil (5-FU) and Cisplatinum(II)—Diamine Dichloride (Cisplatinum as the active ingredient of thedrug formulation cisplatin) upon the immunogenicity of G17DT immunogenin mice.

G17DT immunogen was formulated with Montanide(® ISA 703 at 1.25 mg/ml ofG17DT conjugate. Mice were immunized intraperitoncally (IP) with aninjection volume of 0.1 ml delivering a dose of 125 μg G17DT on days 0,28 and 56. The chemotherapeutic dosing regimen was based on the dosesrecommended for human patients. Thus the combined 5-FU plus Cisplatinumwas administered to the test group on day 0, following by 5-FU above ondays 1 and 2 by intravenous injection in 0.2 ml volume at doses of 10.0mg/kg 5-FU and 1.0 mg/kg Cisplatinum. Control mice were immunized whilereceiving saline vehicle without the chemotherapeutics. As supportivetherapy for the potential dehydration caused by Cisplatinum, all micereceived IP 1.0 ml PSS (Physiological Saline solution). The anti-G17antibody levels in sera collected at 14-day intervals (plus anadditional on d 21) were assayed by ELISA.

The G17 DT immunogen was formulated as described in Example 4. The 5FUand Cisplatinum formulations were prepared at 10.0 mg/kg for 5-FU and1.0 mg/kg for Cisplatinum to provide calculated doses of 320 mg of 5-FUand 32 mg of Cisplatinum. The dry aliquots of 5-FU and Cisplatinum werereconstituted on treatment days by dissolution in the same PSS to yield1.6 mg/ml and 0.16 mg/ml, respectively. For day 1 and 2, 5-FU alone wasgiven at 1.6 mg/ml in PSS.

The subject mice were ten CAPF1 female, about 18 months old. All micewere G17-immunized at a dose (IP) of 0.1 ml of G17 DT on days 0, 28, 56of study. All chemotherapeutics were administered in volumes of 0.2 ml.Control mice received 0.2 ml of PSS placebo, according to the treatmentregimen. To counter Cisplatinum related dehydration, all mice wereinjected IP with 10 ml PSS per mouse. The mice were bled every 14 daysstarting on day 0 and ending on day 84. The sera were assayed by ELISA,showing that all mice responded to G17 DT immunogen with significanttiters of anti-G17 antibodies. The responses of both groups peaked onday 70. The mean/median response of the combination treatment group wasovercome by the administration of the second injection of immunogen. Theresults indicate that the 5FU plus Cisplatinum treatment (following adose regimen designed for humans) had no statistically significantnegative effect on the anti-G17 antibody response. TABLE 2 A Comparisonof Anti-G17 Antibody Mean Titers by ELISA (Ex. 6) (plus/minus S.D.) DAYOF STUDY 0 14 21 28 42 56 70 84 Group 1, 125 μg 100 997 ± 194 1,099 ±249 1,029 ± 355 70,660 ± 30571 48,020 ± 22382  108300 ± 44771  50500 ±11449 Group 2, 125 μg 100 874 ± 222   739 ± 265  266 ± 83 81,400 ± 3442935,966 ± 14014 15,4360 ± 41771 48,860 ± 10797 G17DT, 5-FU-CISPLATINUM Treatment t-test Group 1 vs. 2 0.687 0.351 0.066 0.821 0.660 0.473 0.920P(T <= t) two-tail

EXAMPLE 7

The following clinical treatment regime is provided:

A. Combined Treatment with Immunization and Gemcitabine (Protocol)MEDICATION G17DT Gemcitabine (immunotherapy + Days 1, 28, 56 Day 1 andcontinue once chemotherapy) a week for a total of 7 weeks, followed by 1week rest. Then continue with 4-week cycles of 3 weekly administrations,followed by 1 week rest each cycle. Sampling Schedules: Blood Chemistry:weekly Hematology: weekly Urinalysis: weekly Immunology: bi-weekly toweek 12, monthly after week 12 Diagnostics prior to entry: Endoscopy:pre-enrollment CT scan and Chest x-ray: pre-enrollment Diagnosticsfollow up: CT scan: monthly Chest x-ray: as needed

The treatment(s) can be administered up to disease progression,unacceptable toxicities or withdrawal of consent. If the unacceptabletoxicities are due to chemotherapy and the subject's disease has notprogressed, chemotherapy can be stopped and immunotherapy can becontinued as planned. Immunotherapy is continued after the onset ofdisease progression and is stopped only for unacceptable toxicityattributable to G17DT or withdrawal of consent.

Gemcitabine

-   Dose: 1000 mg/m²-   Route: in 250 ml of 0.9% sodium chloride over 30 min., IV infusion-   Schedule: Day 1 and continue once a week for a total of 7 weeks,    followed by 1 week rest.    Then continue with 4-week cycles of 3 weekly administrations,    followed by 1 week rest each cycle.

Alternatively, the dosage of gemcitabine may be reduced to about 750mg/m² or 500 mg/m² or less.

B. Combination with Irinotecan

Irinotecan was initially approved as second-line therapy for patientswith metastatic colorectal carcinoma whose disease has recurred orprogressed following 5-FU-based therapy. Subsequently, irinotecan incombination with 5-FU and LV was approved as first-line therapy fortreatment of this disease. Irinotecan-based therapy, however, is notwithout significant morbidity, including diarrhea and myelosuppression.To reduce these side effects, dose adjustments are often necessary thatmay reduce the efficacy of irinotecan. Patients who failirinotecan-based therapy, thereby, are left with few options for theefficacious treatment of their disease.

Immunotherapy combined with irinotecan has the potential to enhanceoverall therapeutic effect, while reducing side effects associated withirinotecan treatment. In addition to having antitumor activity on itsown, gastrin neutralization by G17DT administered prior to 5-FU and LVtreatment has been shown to enhance the antitumor activity of 5-FU andLV therapy, and potentiated the activity of suboptimal doses of 5-FU onrat colorectal tumors.

Using this rationale, it can be proposed that G17DT may also potentiatethe efficacy of irinotecan and offer a potentially new treatmentmodality that combines the cytostatic action of antigastrin immunizationwith the cytotoxic effects of chemotherapy. In addition, immunizationwith G17DT could be used with drugs whose maximum doses must be reduceddue to associated serious AEs.

G17DT is administered as an intramuscular injection of 250,μg in 0.2 mLvehicle. To elicit an immune response, G17DT is administered in theinitial treatment period at Week 1. In the absence of Grade 2 or greaterallergic reaction to G17DT following first injection of G17DT,additional doses of G17DT are administered at Weeks 5, 9; thereafterG17DT is administered following a decrease in anti-G17 titer of 50% ormore from the maximum titer.

Irinotecan is administered as an intravenous infusion of 125 mg/m² over90 minutes starting at Week 5 or 4 weeks after the initialadministration of G17DT. Each cycle of treatment consists of irinotecani.v. administration by infusion once weekly for 4 weeks, followed by a2-week rest period. Additional cycles of treatment are repeated untildisease progression, dose limiting toxicity (DLT), or patientwithdrawal. If necessary, doses of irinotecan can be adjusted by usingspecific dose modification rules to accommodate individual patienttolerance of treatment. In the absence of DLT or progressive disease,patients continue the G17DT-irinotecan combination treatment regimen.This dosing regimen is based on results from 3 open-label, single-agentclinical studies involving a total of 304 patients.

EXAMPLE 7 Tumor Response Criteria

Abdominal/pelvic CT scan with IV contrast and chest x-ray (as needed)can be used to assess tumor burden.

Examples of such lesions evaluated by clinical examination or imagingtools include:

-   -   a skin nodule or superficial lymph node minimum ≧10 mm×≧10 mm    -   a liver lesion, soft tissue, lymph node and masses investigated        by CT scan (minimum ≧20 mm×≧10 mm).

These include all the lesions that can be measured with only onediameter ≧20 mm on CT scan or ≧10 mm on physical examination.

An example of these lesions is a palpable abdominal mass or soft tissuemass that can be measured only in one diameter.

EXAMPLE 8 Evaluation of Response

Subjects must have received 3 immunizations with G17DT and/or GRE1DT anda minimum of one 7-week cycle or two 4-week cycles of treatment withgemcitabine with at least one follow-up tumor assessment using the samemethod as baseline to be considered evaluable for response unless “earlyprogression” occurs, in which case they are considered evaluable (inprogressive disease). Subjects on therapy for at least this period havetheir-response classified according to the definitions set out below.

Immune response assessments is made by ELISA on blood samples collectedfrom subjects every 2 weeks up to 12 weeks and every 4 weeks thereafter.Tumor assessment for all lesions must be performed every 4 weeks ontherapy until the documentation of the progression. Tumor-responseshould be reported on follow-up visits every 4 weeks for the subject whogoes off study for reason other than progressive disease (PD).

No further anti-tumor therapy is given after end of treatment untildisease progression is documented, except if the subject requestsfurther therapy or the investigator deems it necessary. All uni- orbi-dimensionally measurable lesions should be measured every subsequent4 weeks. Additional assessments should be performed to confirm aresponse at least 28 days after the first response has been observed. Inaddition, extra assessments may be performed if there is a clinicalsuspicion of progression. When multiple lesions are present, this maynot be possible and, under such circumstances, up to 6 measurable targetlesions which are representative of all organs involved should beselected for the involved sites, giving the priority to bi-dimensionallymeasurable lesions, then uni-dimensionally measurable lesions.

Best overall response is the best response designation recorded from thestart of treatment until disease progression.

Complete and partial responses have to be confirmed by two evaluationsof the disease, taken at least 4 weeks apart (see above for assessmenttime).

No change is only accepted if it is measured at least 4 weeks after thetreatment start.

Tumor response, time to progression, time to treatment failure andsurvival can be analyzed both on an intent-to-treat basis and on theevaluable population.

The period for complete response lasts from the date the completeresponse was achieved to the date thereafter on which progressivedisease is first noted. In those subjects who achieved partial response,only the period of overall response should be recorded. The period ofoverall response lasts from the day of the first observation of response(partial or complete) to the date of first observation of progressivedisease.

Time to disease progression is the time measured from the start oftreatment to the first progression, death, or discontinuation of bothchemotherapy and immunotherapy, whichever occurs first. Subjects thathave not progressed at the time of the final analysis can be censored atthe date of their last tumor assessment. Subjects who receive non-studyanti-tumor therapy before disease progression can be censored at thedate of the last assessment before therapy.

Time to treatment failure is the time measured from the start oftreatment to the date of failure (progression, relapse, death or anyother cause of treatment discontinuation).

Survival is measured from the start of treatment to the date of deathfrom whatever cause. Subjects alive as of the final analysis will becensored at their last contact date.

The pharmacodynamics of the immune response following the primary seriesof three injections are assessed by the proportion of immune responderswith ≧4 ELISA units sustained for 2 consecutive bleeds in study Arm Aattained by week 12 following the first immunization and by the mean andmedian peak titers. Immunoassays are performed by G17 antigen-basedELISA. The quality of the antibody response is measured by inhibitionRIA and assessed by dissociation constant (Kd) and antigen bindingcapacity (ABC), and ABC/Kd ratio.

The mean and median duration of the immune response from peak titer to<25% of peak titer is assayed in order to determine the time toadminister a booster immunization.

Taxanes

Recent treatments of advance prostate cancer include the administrationof chemotherapeutic agents such as taxanes. Taxanes, such as, forexample, docetaxel, are effective microtubule inhibitors therebyinterfering in the further transition of the cell cycle at G2/Mcheck-point. Taxanes have now emerged as a promising class of newlyapproved chemotherapies currently under investigation inhormone-refractory prostate cancer. A number of recent studies indicatethat the taxane, i.e. docetaxel, is particularly active. For example, 35patients with hormone-refractory prostate cancer were treated withdocetaxel at 75 mg/m² every 21 days while being maintained on androgensuppression. Toxicity remained tolerable throughout the treatment;although there were two deaths during the study, one due to lungtoxicity/pneumonia and one due to pulmonary embolus. Responses, definedas a more than 40% PSA decline and a more than 50% reduction ofbi-dimensional cross-products in patients with measurable disease, wereseen in 17 of the 35 patients enrolled, including one complete response.Responses were maintained for a median of nine months (range, 2 to 24months). The median overall survival in this study was 27 months.Preclinical studies suggested a potential benefit for the combination ofdocetaxel with estramustine in the treatment of patients withhormone-refractory prostate cancer. Based on data from two phase Istudies, the docetaxel dose applied for phase II study which wasundertaken in combination with estramustine in human subjects was 70mg/m² or 60 mg/m². Phase II studies of docetaxel plus estramustine havedemonstrated more than 50% PSA declines in 59% to 88% of patients.Although reduction of the dose of estramustine appears to result in asomewhat lower response rate, the contribution of estramuxtine to theefficacy of the docetaxel-estramustine combination was not conclusive.

Passive Immunization:

The chemotherapies described above can be combined with passiveimmunization against cancer growth promoting factors and receptorscomprises administration of purified antibodies which can be polyclonalor monoclonal. Monoclonal antibodies are conventionally prepared fortreatment in humanized or chimeric form.

The transgenic mouse isolated human antibodies can be further modifiedby radiolabel or other toxic materials so as to induce necrosis orapoptosis in the target cancer cells. For example, the antibodies,modified or not, will be directed to bind to receptors, many of whichwill internalize the ab-receptor complex to the nucleus of the cell soas to lead to the affected cell's death, which process may be similar orlike apoptosis. Pancreatic carcinoma treatment can include one or moreof the combinations of chemotherapeutic agents and active or passiveimmunotherapies, as described above. However, the treatment are not inany way limited to the specific aforementioned samples. On the contrary,the thrust of the invention suggests a useful variety of combinedchemical and immunological agents to slow or decrease tumor growth.

Polyclonal antibodies can be obtained from immunized human and othermammalian sources. One manner of inducing high affinity specificantisera utilizes the immunogen as described above where the antigenicvarieties are conjugated to immunogenic carrier. The highly activeantibody fractions are isolated and purified by conventional means forinoculation in the cancer patient in need of this treatment. Since thistype of passive immunotherapy can utilize the patient's own antibodies,the risk of rejection and other complications can be minimized orentirely avoided.

Treatment with modified, such as radioactive-labeled antibodies is fromanti-CCKB/gastrin receptor antibodies would effect cell death byinternalized specific irradiation. Furthermore, the combination therapyusing gastrin and gastrin receptor immunogens can be administered toimmunize or prevent metastasis of gastrin-dependent adenocarcinomacells. Such metastatic cancer cells may derive from gastric, prostate,pancreatic, or colorectal lesions and localize in other tissues, such asbone, liver. or lymph nodes. Anti-gastrin immunization has been shown toinhibit liver metasis.

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1. A combination for use in the treatment of pancreatic cancercomprising: (i) an anti-gastrin effective immunogenic composition; and(ii) one or more chemotherapeutic agents suitable for inhibiting cancergrowth.
 2. The combination of claim 1 wherein the anti-gastrin effectiveimmunogenic composition is selected from immunogens comprising anepitope of the gastrin peptide G17 covalently linked through a spacerpeptide to an immunogenic protein or fragment thereof.
 3. Thecombination of claim 1, which further comprises an anti-CCKB/gastrinreceptor peptide GRE1 or peptide GRE4 effective immunogenic composition.4. The combination of claim 1 wherein one more chemotherapeutic agent isselected from the group consisting of docetaxel,leucovorin/5-florouracil, gemcitabine, cisplatin and irinotecan.
 5. Thecombination of claim 1 wherein the effective immunogenic compositioncomprises a conjugate of the aminoterminal G17 peptide epitopecovalently linked to a seven-amino acid/peptide spacer which is attachedto an ε-amino acid of the side chain of the immunogenic carrier proteinlysine residue.
 6. The combination of claim 3, wherein the effectiveimmunogenic composition comprises a conjugate of the aminoterminalCCK-B/gastric receptor peptide which is attached to an ε-amino acid sidechain of the immunogenic carrier protein lysine residue.
 7. Thecombination of claim 1 wherein the immunogenic composition is formulatedin a water-in-oil emulsion suitable for intramuscular injection.
 8. Thecombination of claim 1, wherein the immunogenic composition ranges from10 μg to 5000 μg of the immuunogen per dose.
 9. The combination of claim1 wherein the chemotherapeutic agent is gemcitabine at a dose rangingfrom 500-1400 mg/m2 weekly for 3 weeks, every 28 days.
 10. Thecombination of claim 1 or 6 wherein the immunogenic composition is about250 μg to 500 μg per dose.
 11. The combination of claim 1 wherein thechemotherapeutic agent is irinotecan.
 12. A combination for use in thetreatment of pancreatic cancer comprising: (i) an anti-gastrin and/oranti-gastrin receptor effective immunological agent which can bemonoclonal antibody or polyclonal antibodies derived from antiseraproduced in a patient by immunization with an anti-gastrin immunogeniccomposition; and (ii) one or more chemotherapeutic agents suitable forinhibiting cancer growth.
 13. (canceled)
 14. A method for treatingpancreatic cancer comprising administering a gastrin-immunoneutralizingimmunogenic composition; and administering a pharmaceutical compositionof one or more chemotherapeutic agent effective for inhibiting cancergrowth.
 15. The method of claim 14 wherein the immunogenic compositioncomprising, an immunogen directed to eliciting neutralizing antibodiesagainst gastrin G17, Gly-G17, CCK-B/gastrin receptor peptide GRE1 orGRE4.
 16. The method of claim 14 wherein one or more chemotherapeuticagent is selected from a group consisting of docetaxcl,leucovorin/5-fluorouracil, gemcitabine, cisplatin and irinotecan. 17.The method of claim 14, wherein the chemotherapeutic agent isgemcitabine.
 18. The combination as claimed in claim 1, wherein thetreatment prevents cancer cell metastasis.
 19. The combination asclaimed in claim 12, wherein the treatment prevents cancer cellmetastasis.